Cardiomyopathy relates to the deterioration of the cardiac muscle of the heart wall. The most common form is dilated cardiomyopathy wherein the heart, particularly the left ventricle, is enlarged and weakened. Often the cause is unknown. This is referred to as idiopathic dilated cardiomyopathy (IDC). IDC and other forms of cardiomyopathy can lead to heart failure, which is a debilitating condition in which abnormal function of the heart leads to inadequate blood flow to fulfill the needs of the tissues and organs of the body. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately fill with blood between heartbeats and the valves regulating blood flow become leaky, allowing regurgitation or back-flow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. A particularly severe form of heart failure is congestive heart failure (CHF) wherein the weak pumping of the heart leads to build-up of fluids in the lungs and other organs and tissues. CHF is often fatal. Hence, cardiomyopathy increases the risk of mortality since it can lead to heart failure. In addition, cardiomyopathy can trigger various life-threatening arrhythmias such as ventricular fibrillation, which can result in sudden cardiac death. As can be appreciated, cardiomyopathy is a potentially serious condition that should be detected and treated as early as possible.
Many patients at risk of cardiomyopathy or heart failure, particularly the elderly, have pacemaker or ICDs implanted therein, or are candidates for such devices. Various techniques have been developed to detect heart failure within a patient using a pacemaker or ICD. See, for example: U.S. patent application Ser. No. 11/100,008, of Koh et al., filed May 11, 2004, entitled “System And Method For Evaluating Heart Failure Using An Implantable Medical Device Based On Heart Rate During Patient Activity”; U.S. patent application Ser. No. 11/100,008, of Kil et al., entitled “System And Method For Detecting Heart Failure And Pulmonary Edema Based On Ventricular End-Diastolic Pressure Using An Implantable Medical Device”, filed Apr. 5, 2005; U.S. patent application Ser. No. 11/014,276, of Min et al., entitled “System And Method For Predicting Heart Failure Based On Ventricular End-Diastolic Volume/Pressure Using An Implantable Medical Device”, filed Dec. 15, 2004; U.S. patent application Ser. No. 10/810,437, of Bornzin et al., entitled “System and Method for Evaluating Heart Failure Based on Ventricular End-Diastolic Volume Using an Implantable Medical Device,” filed Mar. 26, 2004; U.S. patent application Ser. No. 10/346,809, of Min et al., entitled “System and Method for Monitoring Cardiac Function via Cardiac Sounds Using an Implantable Cardiac Stimulation Device,” filed Jan. 17, 2003; and U.S. patent application Ser. No. 10/792,305, filed Mar. 2, 2004, entitled “System And Method For Diagnosing And Tracking Congestive Heart Failure Based On The Periodicity Of Cheyne-Stokes Respiration Using An Implantable Medical Device”. See also: U.S. Pat. No. 6,572,557, to Tchou, et al., entitled “System and Method for Monitoring Progression of Cardiac Disease State Using Physiologic Sensors.” U.S. Pat. No. 6,645,153, to Kroll et al., entitled “System and Method for Evaluating Risk of Mortality Due To Congestive Heart Failure Using Physiologic Sensors”, and U.S. Pat. No. 6,438,408 to Mulligan et al., entitled “Implantable Medical Device For Monitoring Congestive Heart Failure.”
However, heretofore, it does not appear that any viable techniques have been developed for detecting dilated cardiomyopathy using an implanted device, at least before the myopathy progresses to heart failure. Accordingly, it would be highly desirable to provide techniques for detecting and tracking dilated cardiomyopathy using a pacemaker or other implantable medical device, and it is to this end that aspects of the invention are directed. Early detection of dilated cardiomyopathy via an implanted device could significantly improve the patient's long term prognosis. Note, though, that many patients with heart failure do not have dilated cardiomyopathy. Conversely, many patients with dilated cardiomyopathy do not have heart failure. Other patients have both. Accordingly, it would also be desirable to provide techniques for use by an implanted device for distinguishing between dilated cardiomyopathy and heart failure, and it is to this end that other aspects of the invention are directed.